A service robot equipped with a Quectel EG25-GC modem failed to register on Russian mobile networks despite detecting LTE signals. The device, running Android 11 on a Rockchip RK3568 board, could identify operators but remained disconnected.
Investigation revealed that the modem firmware contained specific restrictions for Russia and Iran, as outlined in Quectel's PCN 2022113001 document dated November 30, 2022. These restrictions, effective from February 1, 2023, prevented network attachment.
The research team accessed the modem's internal Linux system via a root shell using the QADBKEY challenge-response mechanism. By analyzing the firmware segments, they identified diagnostic strings explicitly flagging Russian PLMNs as forbidden.
The team decompressed the Qualcomm Hexagon code from the modem.b21 segment using the q6zip format. By mapping the virtual memory range starting at 0xd0000000, they located the specific instruction responsible for the network block.
Modifying the firmware allowed the robot to successfully register on Russian LTE networks. The researchers noted that this process involved manual extraction and analysis of radio segments, and they warned that no universal recovery method exists for this hardware.
